When operating conventional knuckle boom systems today, there are inefficiencies in the system whenever the boom and any lifted load is lowered, i.e. a reduction in their potential energy is dissipated by metering hydraulic oil through an orifice and converting the energy into heat which goes into the machine's hydraulic oil. Cooling systems need to be added to the machine to expel this heat to ambient air so the hydraulic oil does not overheat.
Mechanical-hydraulic systems have inherent kinematic limitations when operated by controlling cylinder speeds. The knuckle boom is a non-linear kinematic system where approximating constant boom system endpoint trajectories and velocities can be challenging. To raise a boom and load, typically diesel fuel or electricity is used as an energy source and converted to hydraulic power through diesel engines, electric motors and/or hydraulic pumps. This energy, in the form of hydraulic oil pressure and flow, is directed to the hydraulic cylinders by control valves which may be commanded by a human operator and/or an automated routine. There can be instances in a boom system where one or more booms are being raised and lowered simultaneously. It would be desirable to transfer energy from the lowering boom(s) and load(s) to the boom(s) and load(s) being raised in all operating modes.